U.S. patent application number 14/161312 was filed with the patent office on 2014-07-31 for cell-specific reference signal interference averaging.
This patent application is currently assigned to QUALCOMM Incorporated. The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Peter GAAL, Tingfang JI, Iyab Issam SAKHNINI.
Application Number | 20140211646 14/161312 |
Document ID | / |
Family ID | 51222848 |
Filed Date | 2014-07-31 |
United States Patent
Application |
20140211646 |
Kind Code |
A1 |
JI; Tingfang ; et
al. |
July 31, 2014 |
CELL-SPECIFIC REFERENCE SIGNAL INTERFERENCE AVERAGING
Abstract
Aspects of the present disclosure provide techniques and
apparatus for enhancing performance by selectively applying
averaging to CSI reporting processes. According to certain aspects,
a base station (e.g., an eNB) with knowledge of traffic patterns of
potentially interfering transmitters may signal a UE how (or
whether) to apply averaging, for example, when reporting CSI based
on interference measurement resources (IMR).
Inventors: |
JI; Tingfang; (San Diego,
CA) ; GAAL; Peter; (San Diego, CA) ; SAKHNINI;
Iyab Issam; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
51222848 |
Appl. No.: |
14/161312 |
Filed: |
January 22, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61756901 |
Jan 25, 2013 |
|
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Current U.S.
Class: |
370/252 |
Current CPC
Class: |
H04W 24/10 20130101;
H04L 43/08 20130101; H04L 43/06 20130101 |
Class at
Publication: |
370/252 |
International
Class: |
H04L 12/26 20060101
H04L012/26 |
Claims
1. A method for wireless communications by a user equipment (UE),
comprising: receiving, from a base station, an indication of a type
of averaging to be applied for channel state information (CSI)
reporting; measuring reference signals received in one or more
subframes; generating a CSI report based on the measurements and
the indicated type of averaging; and sending the CSI report.
2. The method of claim 1, wherein the indication indicates at least
one of: time domain averaging or frequency domain averaging.
3. The method of claim 1, wherein the indication comprises an
indication of whether or not any type of averaging should be
applied at all.
4. The method of claim 1, wherein the indication comprises an
indication of at least one of: interference averaging, channel
averaging, signal to noise ratio (SNR) averaging, or spectral
efficiency averaging.
5. The method of claim 1, wherein the indication is received as
part of a CSI reporting configuration.
6. The method of claim 1, wherein the indication is provided
independently for different interference measurement resources
(IMRs).
7. The method of claim 1, wherein the indication is provided via at
least one of broadcast or dedicated signaling from the base
station.
8. The method of claim 1, wherein different indications are
provided for different CSI processes for a same interference
measurement resource (IMR).
9. The method of claim 1, wherein different indications are
provided for different types of averaging to be applied
independently to different subsets of subframes.
10. The method of claim 9, wherein subframes in a subset are
selected based, at least in part, on traffic load of a
corresponding interfering base station.
11. The method of claim 1, wherein the indication is provided as a
single bit indicating one of two averaging modes.
12. The method of claim 11, wherein the two averaging modes
comprise: a fixed averaging mode wherein averaging is applied
across a limited range of resources; and an less restricted
averaging mode wherein averaging is applied across a wider range of
resources.
13. The method of claim 1, wherein receiving, from the base
station, the indication of a type of averaging to be applied for
CSI reporting comprises: receiving, from the base station,
signaling to associate a reporting process with a certain set of
measurement resources.
14. The method of claim 13, wherein the signaling associates a
periodic CSI measurement process with a measurement subframe
subset.
15. A method for wireless communications by a base station (BS),
comprising: transmitting, to a user equipment (UE), an indication
of a type of averaging to be applied for channel state information
(CSI) reporting; and receiving, from the UE, a CSI report generated
based on reference signal measurements and the indicated type of
averaging.
16. The method of claim 15, wherein the indication indicates at
least one of: time domain averaging or frequency domain
averaging.
17. The method of claim 15, wherein the indication comprises an
indication of whether or not any type of averaging should be
applied at all.
18. The method of claim 15, wherein the indication comprises an
indication of at least one of: interference averaging, channel
averaging, signal to noise ratio (SNR) averaging, or spectral
efficiency averaging.
19. The method of claim 15, wherein indications are transmitted as
part of a CSI reporting configuration.
20. The method of claim 15, wherein the indication is provided
independently for different interference measurement resources
(IMRs).
21. The method of claim 15, wherein the indication is provided via
at least one of broadcast or dedicated signaling from the base
station.
22. The method of claim 15, wherein different indications are
provided for different CSI processes for a same interference
measurement resource (IMR).
23. The method of claim 15, wherein different indications are
provided for different types of averaging to be applied
independently to different subsets of subframes.
24. The method of claim 23, wherein subframes in a subset are
selected based, at least in part, on traffic load of a
corresponding interfering base station.
25. The method of claim 15, wherein the indication is provided as a
single bit indicating one of two averaging modes.
26. The method of claim 25, wherein the two averaging modes
comprise: a fixed averaging mode wherein averaging is applied
across a limited range of resources; and an less restricted
averaging mode wherein averaging is applied across a wider range of
resources.
27. The method of claim 15, wherein transmitting the indication of
the type of averaging to be applied for CSI reporting comprises:
transmitting, to the UE, signaling to associate a reporting process
with a certain set of measurement resources.
28. The method of claim 27, wherein the signaling associates a
periodic CSI measurement process with a measurement subframe
subset.
29. An apparatus for wireless communications by a user equipment
(UE), comprising: means for receiving, from a base station, an
indication of a type of averaging to be applied for channel state
information (CSI) reporting; means for measuring reference signals
received in one or more subframes; means for generating a CSI
report based on the measurements and the indicated type of
averaging; and means for sending the CSI report.
30. An apparatus for wireless communications by a base station
(BS), comprising: means for transmitting, to a user equipment (UE),
an indication of a type of averaging to be applied for channel
state information (CSI) reporting; and means for receiving, from
the UE, a CSI report generated based on reference signal
measurements and the indicated type of averaging.
Description
CLAIM OF PRIORTY UNDER 35 U.S.C. .sctn.119
[0001] This application claims benefit of U.S. Provisional Patent
Application Ser. No. 61/756,901, filed Jan. 25, 2013, which is
herein incorporated by reference in its entirety.
BACKGROUND
[0002] I. Field
[0003] Certain aspects of the present disclosure generally relate
to wireless communications and, more particularly, to cell-specific
reference signal (CRS) interference averaging.
[0004] II. Background
[0005] Wireless communication systems are widely deployed to
provide various types of communication content such as voice, data,
and so on. These systems may be multiple-access systems capable of
supporting communication with multiple users by sharing the
available system resources (e.g., bandwidth and transmit power).
Examples of such multiple-access systems include code division
multiple access (CDMA) systems, time division multiple access
(TDMA) systems, frequency division multiple access (FDMA) systems,
3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)
including LTE-Advanced systems and orthogonal frequency division
multiple access (OFDMA) systems.
[0006] Generally, a wireless multiple-access communication system
can simultaneously support communication for multiple wireless
terminals. Each terminal communicates with one or more base
stations via transmissions on the forward and reverse links. The
forward link (or downlink) refers to the communication link from
the base stations to the terminals, and the reverse link (or
uplink) refers to the communication link from the terminals to the
base stations. This communication link may be established via a
single-input single-output, multiple-input single-output or a
multiple-input multiple-output (MIMO) system.
SUMMARY
[0007] Certain aspects of the present disclosure generally relate
to wireless communications and, more particularly, to cell-specific
reference signal (CRS) interference averaging.
[0008] Certain aspects of the present disclosure provide a method
for wireless communications by a user equipment (UE). The method
generally includes receiving, from a base station, an indication of
a type of averaging to be applied for channel state information
(CSI) reporting, measuring reference signals received in one or
more subframes, generating a CSI report based on the measurements
and the indicated type of averaging, and sending the CSI
report.
[0009] Certain aspects of the present disclosure provide a method
for wireless communications by a base station (BS). The method
generally includes transmitting, to a user equipment (UE), an
indication of a type of averaging to be applied for channel state
information (CSI) reporting and receiving, from the UE, a CSI
report generated based on reference signal measurements and the
indicated type of averaging.
[0010] Certain aspects of the present disclosure provide an
apparatus for wireless communications by a user equipment (UE). The
apparatus generally includes means for receiving, from a base
station, an indication of a type of averaging to be applied for
channel state information (CSI) reporting, means for measuring
reference signals received in one or more subframes, means for
generating a CSI report based on the measurements and the indicated
type of averaging, and means for sending the CSI report.
[0011] Certain aspects of the present disclosure provide an
apparatus for wireless communications by a base station (BS). The
apparatus generally includes means for transmitting, to a user
equipment (UE), an indication of a type of averaging to be applied
for channel state information (CSI) reporting and means for
receiving, from the UE, a CSI report generated based on reference
signal measurements and the indicated type of averaging.
[0012] Certain aspects of the present disclosure also provide
apparatuses and program products for performing the operations
described above.
[0013] Various aspects and features of the disclosure are described
in further detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] So that the manner in which the above-recited features of
the present disclosure can be understood in detail, a more
particular description, briefly summarized above, may be had by
reference to aspects, some of which are illustrated in the appended
drawings. It is to be noted, however, that the appended drawings
illustrate only certain typical aspects of this disclosure and are
therefore not to be considered limiting of its scope, for the
description may admit to other equally effective aspects.
[0015] FIG. 1 is a block diagram conceptually illustrating an
example wireless communication network, in accordance with certain
aspects of the present disclosure.
[0016] FIG. 2 is a block diagram conceptually illustrating an
example of an evolved node B (eNB) in communication with a user
equipment (UE) in a wireless communications network, in accordance
with certain aspects of the present disclosure.
[0017] FIG. 3 is a block diagram conceptually illustrating an
example frame structure for a particular radio access technology
(RAT) for use in a wireless communications network, in accordance
with certain aspects of the present disclosure.
[0018] FIG. 4 illustrates an example subframe format for the
downlink with normal cyclic prefix (CP), in accordance with certain
aspects of the present disclosure.
[0019] FIGS. 5-8 illustrate an example gains achieved with channel
state information (CSI) filtering, in accordance with certain
aspects of the present disclosure.
[0020] FIGS. 9-10 illustrate example CQI histograms, in accordance
with certain aspects of the present disclosure.
[0021] FIG. 11 illustrates example operations which may be
performed by a UE, in accordance with certain aspects of the
present disclosure.
[0022] FIG. 12 illustrates example operations which may be
performed by base station (BS), in accordance with certain aspects
of the present disclosure.
DETAILED DESCRIPTION
[0023] Aspects of the present disclosure provide techniques and
apparatus for enhancing performance by selectively applying
averaging to CSI reporting processes. According to certain aspects,
a base station (e.g., an eNB) with knowledge of traffic patterns of
potentially interfering transmitters may signal a UE how (or
whether) to apply averaging, for example, when reporting CSI based
on interference measurement resources (IMR). As a result, the
report may provide a more useful measurement of actual
interference.
[0024] Various aspects of the disclosure are described more fully
hereinafter with reference to the accompanying drawings. This
disclosure may, however, be embodied in many different forms and
should not be construed as limited to any specific structure or
function presented throughout this disclosure. Rather, these
aspects are provided so that this disclosure will be thorough and
complete, and will fully convey the scope of the disclosure to
those skilled in the art. Based on the teachings herein one skilled
in the art should appreciate that the scope of the disclosure is
intended to cover any aspect of the disclosure disclosed herein,
whether implemented independently of or combined with any other
aspect of the disclosure. For example, an apparatus may be
implemented or a method may be practiced using any number of the
aspects set forth herein. In addition, the scope of the disclosure
is intended to cover such an apparatus or method which is practiced
using other structure, functionality, or structure and
functionality in addition to or other than the various aspects of
the disclosure set forth herein. It should be understood that any
aspect of the disclosure disclosed herein may be embodied by one or
more elements of a claim.
[0025] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any aspect described herein as
"exemplary" is not necessarily to be construed as preferred or
advantageous over other aspects.
[0026] Although particular aspects are described herein, many
variations and permutations of these aspects fall within the scope
of the disclosure. Although some benefits and advantages of the
preferred aspects are mentioned, the scope of the disclosure is not
intended to be limited to particular benefits, uses, or objectives.
Rather, aspects of the disclosure are intended to be broadly
applicable to different wireless technologies, system
configurations, networks, and transmission protocols, some of which
are illustrated by way of example in the figures and in the
following description of the preferred aspects. The detailed
description and drawings are merely illustrative of the disclosure
rather than limiting, the scope of the disclosure being defined by
the appended claims and equivalents thereof.
[0027] The techniques described herein may be used for various
wireless communication networks such as CDMA, TDMA, FDMA, OFDMA,
SC-FDMA and other networks. The terms "network" and "system" are
often used interchangeably. A CDMA network may implement a radio
technology such as Universal Terrestrial Radio Access (UTRA),
cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other
variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856
standards. A TDMA network may implement a radio technology such as
Global System for Mobile Communications (GSM). An OFDMA network may
implement a radio technology such as Evolved UTRA (E-UTRA), Ultra
Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),
IEEE 802.20, Flash-OFDM.RTM., etc. UTRA and E-UTRA are part of
Universal Mobile Telecommunication System (UMTS). 3GPP Long Term
Evolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS
that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are
described in documents from an organization named "3rd Generation
Partnership Project" (3GPP). cdma2000 and UMB are described in
documents from an organization named "3rd Generation Partnership
Project 2" (3GPP2).
[0028] Single carrier frequency division multiple access (SC-FDMA)
is a transmission technique that utilizes single carrier modulation
at a transmitter side and frequency domain equalization at a
receiver side. The SC-FDMA has similar performance and essentially
the same overall complexity as those of OFDMA system. However,
SC-FDMA signal has lower peak-to-average power ratio (PAPR) because
of its inherent single carrier structure. The SC-FDMA has drawn
great attention, especially in the uplink communications where
lower PAPR greatly benefits the mobile terminal in terms of
transmit power efficiency. It is currently a working assumption for
uplink multiple access scheme in the 3GPP LTE and the Evolved
UTRA.
[0029] A base station ("BS") may comprise, be implemented as, or
known as NodeB, Radio Network Controller ("RNC"), Evolved NodeB
(eNodeB), Base Station Controller ("BSC"), Base Transceiver Station
("BTS"), Base Station ("BS"), Transceiver Function ("TF"), Radio
Router, Radio Transceiver, Basic Service Set ("BSS"), Extended
Service Set ("ESS"), Radio Base Station ("RBS"), or some other
terminology.
[0030] A user equipment (UE) may comprise, be implemented as, or
known as an access terminal, a subscriber station, a subscriber
unit, a remote station, a remote terminal, a mobile station, a user
agent, a user device, user equipment, a user station, or some other
terminology. In some implementations, mobile station may comprise a
cellular telephone, a cordless telephone, a Session Initiation
Protocol ("SIP") phone, a wireless local loop ("WLL") station, a
personal digital assistant ("PDA"), a handheld device having
wireless connection capability, a Station ("STA"), or some other
suitable processing device connected to a wireless modem.
Accordingly, one or more aspects taught herein may be incorporated
into a phone (e.g., a cellular phone or smart phone), a computer
(e.g., a laptop), a portable communication device, a portable
computing device (e.g., a personal data assistant), an
entertainment device (e.g., a music or video device, or a satellite
radio), a global positioning system device, or any other suitable
device that is configured to communicate via a wireless or wired
medium. In some aspects, the node is a wireless node. Such wireless
node may provide, for example, connectivity for or to a network
(e.g., a wide area network such as the Internet or a cellular
network) via a wired or wireless communication link.
[0031] The techniques described herein may be used for the wireless
networks and radio technologies mentioned above as well as other
wireless networks and radio technologies. For clarity, certain
aspects of the techniques are described below for LTE, and LTE
terminology is used in much of the description below.
An Example Wireless Communication Systems
[0032] FIG. 1 shows a wireless communication network 100, which may
be an LTE network or some other wireless network. Wireless network
100 may include a number of evolved Node Bs (eNBs) 110 and other
network entities. An eNB is an entity that communicates with user
equipments (UEs) and may also be referred to as a base station, a
Node B, an access point (AP), etc. Each eNB may provide
communication coverage for a particular geographic area. In 3GPP,
the term "cell" can refer to a coverage area of an eNB and/or an
eNB subsystem serving this coverage area, depending on the context
in which the term is used.
[0033] An eNB may provide communication coverage for a macro cell,
a pico cell, a femto cell, and/or other types of cell. A macro cell
may cover a relatively large geographic area (e.g., several
kilometers in radius) and may allow unrestricted access by UEs with
service subscription. A pico cell may cover a relatively small
geographic area and may allow unrestricted access by UEs with
service subscription. A femto cell may cover a relatively small
geographic area (e.g., a home) and may allow restricted access by
UEs having association with the femto cell (e.g., UEs in a closed
subscriber group (CSG)). An eNB for a macro cell may be referred to
as a macro eNB. An eNB for a pico cell may be referred to as a pico
eNB. An eNB for a femto cell may be referred to as a femto eNB or a
home eNB (HeNB). In the example shown in FIG. 1, an eNB 110a may be
a macro eNB for a macro cell 102a, an eNB 110b may be a pico eNB
for a pico cell 102b, and an eNB 110c may be a femto eNB for a
femto cell 102c. An eNB may support one or multiple (e.g., three)
cells. The terms "eNB", "base station," and "cell" may be used
interchangeably herein.
[0034] Wireless network 100 may also include relay stations. A
relay station is an entity that can receive a transmission of data
from an upstream station (e.g., an eNB or a UE) and send a
transmission of the data to a downstream station (e.g., a UE or an
eNB). A relay station may also be a UE that can relay transmissions
for other UEs. In the example shown in FIG. 1, a relay station 110d
may communicate with macro eNB 110a and a UE 120d in order to
facilitate communication between eNB 110a and UE 120d. A relay
station may also be referred to as a relay eNB, a relay base
station, a relay, etc.
[0035] Wireless network 100 may be a heterogeneous network that
includes eNBs of different types, e.g., macro eNBs, pico eNBs,
femto eNBs, relay eNBs, etc. These different types of eNBs may have
different transmit power levels, different coverage areas, and
different impact on interference in wireless network 100. For
example, macro eNBs may have a high transmit power level (e.g., 5
to 40 W) whereas pico eNBs, femto eNBs, and relay eNBs may have
lower transmit power levels (e.g., 0.1 to 2 W).
[0036] A network controller 130 may couple to a set of eNBs and may
provide coordination and control for these eNBs. Network controller
130 may communicate with the eNBs via a backhaul. The eNBs may also
communicate with one another, e.g., directly or indirectly via a
wireless or wireline backhaul.
[0037] UEs 120 (e.g., 120a, 120b, 120c) may be dispersed throughout
wireless network 100, and each UE may be stationary or mobile. A UE
may also be referred to as an access terminal, a terminal, a mobile
station (MS), a subscriber unit, a station (STA), etc. A UE may be
a cellular phone, a personal digital assistant (PDA), a wireless
modem, a wireless communication device, a handheld device, a laptop
computer, a cordless phone, a wireless local loop (WLL) station, a
tablet, a smart phone, a netbook, a smartbook, etc.
[0038] FIG. 2 is a block diagram of a design of base station/eNB
110 and UE 120, which may be one of the base stations/eNBs and one
of the UEs in FIG. 1. Base station 110 may be equipped with T
antennas 234a through 234t, and UE 120 may be equipped with R
antennas 252a through 252r, where in general T.gtoreq.1 and
R.gtoreq.1.
[0039] At base station 110, a transmit processor 220 may receive
data from a data source 212 for one or more UEs, select one or more
modulation and coding schemes (MCSs) for each UE based on channel
quality indicators (CQIs) received from the UE, process (e.g.,
encode and modulate) the data for each UE based on the MCS(s)
selected for the UE, and provide data symbols for all UEs. Transmit
processor 220 may also process system information (e.g., for
semi-static resource partitioning information (SRPI), etc.) and
control information (e.g., CQI requests, grants, upper layer
signaling, etc.) and provide overhead symbols and control symbols.
Processor 220 may also generate reference symbols for reference
signals (e.g., the common reference signal (CRS)) and
synchronization signals (e.g., the primary synchronization signal
(PSS) and secondary synchronization signal (SSS)). A transmit (TX)
multiple-input multiple-output (MIMO) processor 230 may perform
spatial processing (e.g., precoding) on the data symbols, the
control symbols, the overhead symbols, and/or the reference
symbols, if applicable, and may provide T output symbol streams to
T modulators (MODs) 232a through 232t. Each modulator 232 may
process a respective output symbol stream (e.g., for OFDM, etc.) to
obtain an output sample stream. Each modulator 232 may further
process (e.g., convert to analog, amplify, filter, and upconvert)
the output sample stream to obtain a downlink signal. T downlink
signals from modulators 232a through 232t may be transmitted via T
antennas 234a through 234t, respectively.
[0040] At UE 120, antennas 252a through 252r may receive the
downlink signals from base station 110 and/or other base stations
and may provide received signals to demodulators (DEMODs) 254a
through 254r, respectively. Each demodulator 254 may condition
(e.g., filter, amplify, downconvert, and digitize) its received
signal to obtain input samples. Each demodulator 254 may further
process the input samples (e.g., for OFDM, etc.) to obtain received
symbols. A MIMO detector 256 may obtain received symbols from all R
demodulators 254a through 254r, perform MIMO detection on the
received symbols if applicable, and provide detected symbols. A
receive processor 258 may process (e.g., demodulate and decode) the
detected symbols, provide decoded data for UE 120 to a data sink
260, and provide decoded control information and system information
to a controller/processor 280. A channel processor may determine
reference signal received power (RSRP), received signal strength
indicator (RSSI), reference signal received quality (RSRQ), CQI,
etc.
[0041] On the uplink, at UE 120, a transmit processor 264 may
receive and process data from a data source 262 and control
information (e.g., for reports comprising RSRP, RSSI, RSRQ, CQI,
etc.) from controller/processor 280. Processor 264 may also
generate reference symbols for one or more reference signals. The
symbols from transmit processor 264 may be precoded by a TX MIMO
processor 266 if applicable, further processed by modulators 254a
through 254r (e.g., for SC-FDM, OFDM, etc.), and transmitted to
base station 110. At base station 110, the uplink signals from UE
120 and other UEs may be received by antennas 234, processed by
demodulators 232, detected by a MIMO detector 236 if applicable,
and further processed by a receive processor 238 to obtain decoded
data and control information sent by UE 120. Processor 238 may
provide the decoded data to a data sink 239 and the decoded control
information to controller/processor 240. Base station 110 may
include communication unit 244 and communicate to network
controller 130 via communication unit 244. Network controller 130
may include communication unit 294, controller/processor 290, and
memory 292.
[0042] Controllers/processors 240 and 280 may direct the operation
at base station 110 and UE 120, respectively. Processor 240 and/or
other processors and modules at base station 110, and/or processor
280 and/or other processors and modules at UE 120, may perform or
direct processes for the techniques described herein. Memories 242
and 282 may store data and program codes for base station 110 and
UE 120, respectively. A scheduler 246 may schedule UEs for data
transmission on the downlink and/or uplink.
[0043] When transmitting data to the UE 120, the base station 110
may be configured to determine a bundling size based at least in
part on a data allocation size and precode data in bundled
contiguous resource blocks of the determined bundling size, wherein
resource blocks in each bundle may be precoded with a common
precoding matrix. That is, reference signals (RSs) such as UE-RS
and/or data in the resource blocks may be precoded using the same
precoder. The power level used for the UE-RS in each resource block
(RB) of the bundled RBs may also be the same.
[0044] The UE 120 may be configured to perform complementary
processing to decode data transmitted from the base station 110.
For example, the UE 120 may be configured to determine a bundling
size based on a data allocation size of received data transmitted
from a base station in bundles of contiguous RBs, wherein at least
one reference signal in resource blocks in each bundle are precoded
with a common precoding matrix, estimate at least one precoded
channel based on the determined bundling size and one or more RSs
transmitted from the base station, and decode the received bundles
using the estimated precoded channel.
[0045] FIG. 3 shows an exemplary frame structure 300 for FDD in
LTE. The transmission timeline for each of the downlink and uplink
may be partitioned into units of radio frames. Each radio frame may
have a predetermined duration (e.g., 10 milliseconds (ms)) and may
be partitioned into 10 subframes with indices of 0 through 9. Each
subframe may include two slots. Each radio frame may thus include
20 slots with indices of 0 through 19. Each slot may include L
symbol periods, e.g., seven symbol periods for a normal cyclic
prefix (as shown in FIG. 2) or six symbol periods for an extended
cyclic prefix. The 2L symbol periods in each subframe may be
assigned indices of 0 through 2L-1.
[0046] In LTE, an eNB may transmit a primary synchronization signal
(PSS) and a secondary synchronization signal (SSS) on the downlink
in the center 1.08 MHz of the system bandwidth for each cell
supported by the eNB. The PSS and SSS may be transmitted in symbol
periods 6 and 5, respectively, in subframes 0 and 5 of each radio
frame with the normal cyclic prefix, as shown in FIG. 3. The PSS
and SSS may be used by UEs for cell search and acquisition. The eNB
may transmit a cell-specific reference signal (CRS) across the
system bandwidth for each cell supported by the eNB. The CRS may be
transmitted in certain symbol periods of each subframe and may be
used by the UEs to perform channel estimation, channel quality
measurement, and/or other functions. The eNB may also transmit a
physical broadcast channel (PBCH) in symbol periods 0 to 3 in slot
1 of certain radio frames. The PBCH may carry some system
information. The eNB may transmit other system information such as
system information blocks (SIBs) on a physical downlink shared
channel (PDSCH) in certain subframes. The eNB may transmit control
information/data on a physical downlink control channel (PDCCH) in
the first B symbol periods of a subframe, where B may be
configurable for each subframe. The eNB may transmit traffic data
and/or other data on the PDSCH in the remaining symbol periods of
each subframe.
[0047] The PSS, SSS, CRS, and PBCH in LTE are described in 3GPP TS
36.211, entitled "Evolved Universal Terrestrial Radio Access
(E-UTRA); Physical Channels and Modulation," which is publicly
available.
[0048] FIG. 4 shows two example subframe formats 410 and 420 for
the downlink with a normal cyclic prefix. The available time
frequency resources for the downlink may be partitioned into
resource blocks. Each resource block may cover 12 subcarriers in
one slot and may include a number of resource elements. Each
resource element may cover one subcarrier in one symbol period and
may be used to send one modulation symbol, which may be a real or
complex value.
[0049] Subframe format 410 may be used for an eNB equipped with two
antennas. A CRS may be transmitted from antennas 0 and 1 in symbol
periods 0, 4, 7, and 11. A reference signal is a signal that is
known a priori by a transmitter and a receiver and may also be
referred to as pilot. A CRS is a reference signal that is specific
for a cell, e.g., generated based on a cell identity (ID). In FIG.
4, for a given resource element with label Ra, a modulation symbol
may be transmitted on that resource element from antenna a, and no
modulation symbols may be transmitted on that resource element from
other antennas. Subframe format 420 may be used for an eNB equipped
with four antennas. A CRS may be transmitted from antennas 0 and 1
in symbol periods 0, 4, 7, and 11 and from antennas 2 and 3 in
symbol periods 1 and 8. For both subframe formats 410 and 420, a
CRS may be transmitted on evenly spaced subcarriers, which may be
determined based on cell ID. Different eNBs may transmit their CRSs
on the same or different subcarriers, depending on their cell IDs.
For both subframe formats 410 and 420, resource elements not used
for the CRS may be used to transmit data (e.g., traffic data,
control data, and/or other data).
[0050] An interlace structure may be used for each of the downlink
and uplink for FDD in LTE. For example, Q interlaces with indices
of 0 through Q-1 may be defined, where Q may be equal to 4, 6, 8,
10, or some other value. Each interlace may include subframes that
are spaced apart by Q frames. In particular, interlace q may
include subframes q, q+Q, q+2Q, etc., where q .di-elect cons.{0, .
. . , Q-1}.
[0051] The wireless network may support hybrid automatic
retransmission request (HARQ) for data transmission on the downlink
and uplink. For HARQ, a transmitter (e.g., an eNB 110) may send one
or more transmissions of a packet until the packet is decoded
correctly by a receiver (e.g., a UE 120) or some other termination
condition is encountered. For synchronous HARQ, all transmissions
of the packet may be sent in subframes of a single interlace. For
asynchronous HARQ, each transmission of the packet may be sent in
any subframe.
[0052] A UE may be located within the coverage of multiple eNBs.
One of these eNBs may be selected to serve the UE. The serving eNB
may be selected based on various criteria such as received signal
strength, received signal quality, path loss, etc. Received signal
quality may be quantified by a signal-to-interference-plus-noise
ratio (SINR), or a reference signal received quality (RSRQ), or
some other metric. The UE may operate in a dominant interference
scenario in which the UE may observe high interference from one or
more interfering eNBs.
Example Cell-Specific Reference Signal Interference Averaging
[0053] In certain systems (e.g., long term evolution (LTE) Release
11), channel state information-interference measurement (CSI-IM)
resources can assist the user equipment (UE) for better
interference estimation and measurements. The measurement interval
for CSI-IM resources may be a UE implementation.
[0054] When the interference is measured based on resources
occupied by the interferer's data transmission, the measurement can
show wide variation according to the interferer's traffic load. In
this case, the measured interference may not be well correlated
with the interference in a particular scheduled subframe. To reduce
the discrepancy caused by the interference variations, it is
beneficial for the UE to average the measured interference.
[0055] However, in a system where the scheduler is aware of the
interferer's traffic pattern, the measured interference can be well
correlated with scheduled subframes by associating measurement
subframes with scheduling subframes that are experiencing the same
type of interfering traffic. In this case, it is not beneficial to
average measured interference by the UE.
[0056] Since the UE cannot determine itself whether the scheduler
(eNB) is aware of the interferer's traffic, the UE is not able to
determine the best averaging strategy without assistance from the
eNB.
[0057] Therefore, according to certain aspects of the present
disclosure, a base station (eNB) may provide a UE with an
indication of a type of averaging (and/or whether to average). In
some embodiments, the eNB may send signaling to indicate what type
of averaging should be followed by the UE for the CSI report. The
averaging may refer to one or more of the following: interference
averaging, channel averaging, signal-to-noise ratio (SNR)
averaging, and spectral efficiency averaging.
[0058] The averaging type can indicate either or both of
time-domain averaging and frequency-domain averaging. The signaling
may be either dedicated or broadcast, with dedicated signaling
possibly being more efficient and flexible.
[0059] An efficient signaling can be a single bit indication,
indicating one of two different averaging modes. For example, a
single bit may indicate the UE should use a limited, fixed
averaging (e.g., one subframe or one physical resource block (PRB))
or a less restricted (or unrestricted) averaging.
[0060] According to certain aspects, for CSI-IM, interference may
be measured on specific resources signaled to the UE. When the CSI
report indicates that periodicity and timing can be aligned with
the CSI-IM resources of interest, no further signaling beyond the
averaging indication may be used. However, this may introduce undue
restriction, for example, the UE report may be restricted to
specific subframes only.
[0061] According to certain aspects, the eNB may send additional
signaling to associate a reporting process with a certain set of
measurement resources, thereby decoupling the time of measurement
from the time of sending the report.
[0062] According to certain aspects, a periodic CSI measurement
process may be associated with a measurement subframe subset by
radio resource control (RRC) signaling. In aspects, the averaging
indicator may further control whether the UE should average within
the subframe subset or not.
[0063] For CRS-based modes, FIGS. 5-8 illustrates example gains
which may be achieved with CSI filtering for UE link level
simulations, in accordance with certain aspects of the present
disclosure. FIGS. 5-8 show physical downlink shared channel (PDSCH)
throughput versus SNR for 1 cell TM2 serving 500, 1 cell TM6
serving 600, 2 cell TM2 serving 700, and 2 cell TM6 serving 800,
respectively. One curve each graph shows gains with CSI filtering
502, 602, 702, 802 and the other curve shows gains without CSI
filtering 504, 604, 704, 804. FIGS. 5-8 show example link level
simulation results for additive white Gaussian noise (AWGN) and
explicit interferer with 50% loading. It can be seen that
interferer filtering (in time domain) increases the performance
drastically. Frequency domain filtering is fixed for all
scenarios.
[0064] In the case of AWGN interferer, filtering may account for
channel variations and help reduce the SNR (CQI) variance. This may
help in preventing overshooting the CQI with higher block error
rate (BLER) and lower overall performance. In the case of an
explicit interferer, filtering may reduce the variance of SNR (CQI)
and prevents CQI overshooting. In the 50% loading case, it may
reduce channel and interference variations.
[0065] FIGS. 9 and 10 illustrate example CQI histograms for one
cell TM2 serving 900 and two cell TM2 serving 1000, in accordance
with certain aspects of the present disclosure. FIGS. 9 and 10 each
include a bar showing gains with CQI filtering and one bar showing
gains without CQI filtering. It can be seen that the high CQI
values (which can result in high BLER and impact performance) are
reduced.
[0066] In aspects, using RS-based modes, CSI filtering may reduce
the channel and interferer variations and help reduce the SNR (CQI)
variance resulting in fewer instances where the CQI can overshoot
increasing the BLER and reducing performance. In aspects, using
CSI-RS and CSI-IM modes, UE may be configured to report multiple
CSI reports measuring different interference structures. Filtering
CSI in these cases relies heavily on the level of transmission
point coordination.
[0067] According to certain aspects, where tight transmission point
(TP) coordination is implemented across a large geographical area,
UE CSI filtering may not be used. The interference may be
controlled by the network and the UE can rely on this coordination.
It may be desirable for the network to know exactly what
interference the UE is seeing per CSI report without any
significant time or frequency filtering to better decide on TP
scheduling. Filtering in these cases may not give the network a
true picture of the interference as the CQI can become noisy and
not reflective of the latest measurement. In aspects, UE CSI
filtering may not be used for CSI-RS and CSI-IM based modes where
tight TP coordination and minimal uncontrolled interference
exists.
[0068] According to certain aspects, where tight TP coordination is
not implemented or coordinated multipoint (CoMP) cluster size is
moderate, UE CSI filtering can help with the performance. In CoMP
scenarios 1, 2, 3, and 4, the cluster size may be limited to 1, 3,
or 9 macro cells; hence, residual interference outside the CoMP
cluster could be significant for many UEs. These UEs can benefit
from CSI filtering to control the interference variation. This is
similar to the CRS-based modes, where CSI filtering increases the
performance by reducing the channel and interferer variations and
helps control the SNR and CQI sent to the network.
[0069] In aspects, UE CSI filtering may be desirable for CSI-RS and
CSI-IM based modes where tight TP coordination is absent or
significant uncontrolled interference exists.
[0070] It can be seen that the effect of having or not having UE
CSI filtering is not the same in all cases. There might be cases
where filtering is not desirable and cases where it is desirable.
This can depend on the coordination level as well as the network
control on the interference.
[0071] For CSI-RS and CSI-IM based modes, UE CSI filtering can help
in certain scenarios, and may not help in others. In aspects, for
CSI-RS/CSI-IM based modes, the network may signal the filtering
behavior to the UE based on the deployment and the network
knowledge of the interference structure. This may help the UE in
achieving the maximum performance in all conditions. In aspects,
the network may send signaling information to the UE specifying the
filtering behavior needed based on the deployment and the network
knowledge of the interference structure.
[0072] FIG. 11 illustrates example operations 1100, in accordance
with certain aspects of the present disclosure. The operations 1100
may be performed, for example, by a UE. The operations 1100 may
begin, at 1102, by receiving, from a base station, an indication of
a type of averaging to be applied for channel state information
(CSI) reporting.
[0073] At 1104, the UE may measure reference signals received in
one or more subframes.
[0074] At 1106, the UE may generate a CSI report based on the
measurements and the indicated type of averaging and may send the
report, at 1008.
[0075] FIG. 12 illustrates example operations 1200, in accordance
with certain aspects of the present disclosure. The operations 1200
may be performed, for example, by a base station. The operations
1200 may begin, at 1202, by transmitting, to a user equipment (UE),
an indication of a type of averaging to be applied for channel
state information (CSI) reporting.
[0076] At 1204, the BS may receive, from the UE, a CSI report
generated based on reference signal measurements and the indicated
type of averaging.
[0077] As noted above, the indication of what type of averaging to
use may indicate time domain averaging, frequency domain averaging,
or no averaging. Further, the indication may indicate at least one
of: interference averaging, channel averaging, signal to noise
ratio (SNR) averaging, or spectral efficiency averaging.
[0078] The indication may be signaled in various ways. In some
cases, the indication may be sent as part of a CSI reporting
configuration. In some cases, separate indications may be provided
independently for different interference measurement resources
(IMRs). The indication may be provided via broadcast or dedicated
signaling from the base station. Different indications may be
provided for different CSI processes for a same interference
measurement resource (IMR).
[0079] Further, different indications may be provided for different
types of averaging to be applied independently to different subsets
of subframes. For example, subframes in a subset may be selected
based, at least in part, on traffic load of a corresponding
interfering base station.
[0080] As described above, the indication may be provided as a
single bit indicating one of two averaging modes. The two averaging
modes may include a fixed averaging mode wherein averaging is
applied across a limited range of resources and a less restricted
averaging mode wherein averaging is applied across a wider range of
resources.
[0081] In some cases, the indication may associate a reporting
process with a certain set of measurement resources. For example,
the indication may associate a periodic CSI measurement process
with a measurement subframe subset.
[0082] The various operations of methods described above may be
performed by any suitable means capable of performing the
corresponding functions. The means may include various hardware
and/or software/firmware component(s) and/or module(s), including,
but not limited to a circuit, an application specific integrated
circuit (ASIC), or processor. Generally, where there are operations
illustrated in the Figures, those operations may be performed by
any suitable corresponding counterpart means-plus-function
components.
[0083] It is understood that the specific order or hierarchy of
steps in the processes disclosed is an example of exemplary
approaches. Based upon design preferences, it is understood that
the specific order or hierarchy of steps in the processes may be
rearranged while remaining within the scope of the present
disclosure. The accompanying method claims present elements of the
various steps in a sample order, and are not meant to be limited to
the specific order or hierarchy presented.
[0084] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or combinations
thereof.
[0085] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the disclosure herein may be
implemented as electronic hardware, software/firmware, or
combinations thereof. To clearly illustrate this interchangeability
of hardware and software, various illustrative components, blocks,
modules, circuits, and steps have been described above generally in
terms of their functionality. Whether such functionality is
implemented as hardware or software/firmware depends upon the
particular application and design constraints imposed on the
overall system. Skilled artisans may implement the described
functionality in varying ways for each particular application, but
such implementation decisions should not be interpreted as causing
a departure from the scope of the present disclosure.
[0086] The various illustrative logical blocks, modules, and
circuits described in connection with the disclosure herein may be
implemented or performed with a general-purpose processor, a
digital signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array (FPGA) or other
programmable logic device (PLD), discrete gate or transistor logic,
discrete hardware components, or any combination thereof designed
to perform the functions described herein. A general-purpose
processor may be a microprocessor, but in the alternative, the
processor may be any conventional processor, controller,
microcontroller, or state machine. A processor may also be
implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0087] The steps of a method or algorithm described in connection
with the disclosure herein may be embodied directly in hardware, in
a software/firmware module executed by a processor, or in a
combination thereof A software/firmware module may reside in RAM
memory, flash memory, ROM memory, EPROM memory, EEPROM memory,
registers, hard disk, a removable disk, a CD-ROM, or any other form
of storage medium known in the art. An exemplary storage medium is
coupled to the processor such that the processor can read
information from, and write information to, the storage medium. In
the alternative, the storage medium may be integral to the
processor. The processor and the storage medium may reside in an
ASIC. The ASIC may reside in a user terminal In the alternative,
the processor and the storage medium may reside as discrete
components in a user terminal.
[0088] In one or more exemplary designs, the functions described
may be implemented in hardware, software/firmware, or combinations
thereof. If implemented in software, the functions may be stored on
or transmitted over as one or more instructions or code on a
computer-readable medium. Computer-readable media include both
computer storage media and communication media including any medium
that facilitates transfer of a computer program from one place to
another. A storage medium may be any available medium that can be
accessed by a general purpose or special purpose computer. By way
of example, and not limitation, such computer-readable media can
comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage,
magnetic disk storage or other magnetic storage devices, or any
other medium that can be used to carry or store desired program
code means in the form of instructions or data structures and that
can be accessed by a general-purpose or special-purpose computer,
or a general-purpose or special-purpose processor. Also, any
connection is properly termed a computer-readable medium. For
example, if the software is transmitted from a website, server, or
other remote source using a coaxial cable, fiber optic cable,
twisted pair, digital subscriber line (DSL), or wireless
technologies such as infrared, radio, and microwave, then the
coaxial cable, fiber optic cable, twisted pair, DSL, or wireless
technologies such as infrared, radio, and microwave are included in
the definition of medium. Disk and disc, as used herein, includes
compact disc (CD), laser disc, optical disc, digital versatile disc
(DVD), floppy disk and Blu-ray disc where disks usually reproduce
data magnetically, while discs reproduce data optically with
lasers. Thus, in some aspects computer-readable media may comprise
non-transitory computer-readable media (e.g., tangible media). In
addition, for other aspects computer-readable media may comprise
transitory computer-readable media (e.g., a signal). Combinations
of the above should also be included within the scope of
computer-readable media.
[0089] As used herein, a phrase referring to "at least one of" a
list of items refers to any combination of those items, including
single members. As an example, "at least one of a, b, or c" is
intended to cover a, b, c, a-b, a-c, b-c, and a-b-c.
[0090] The previous description of the disclosure is provided to
enable any person skilled in the art to make or use the disclosure.
Various modifications to the disclosure will be readily apparent to
those skilled in the art, and the generic principles defined herein
may be applied to other variations without departing from the
spirit or scope of the disclosure. Thus, the disclosure is not
intended to be limited to the examples and designs described herein
but is to be accorded the widest scope consistent with the
principles and novel features disclosed herein.
* * * * *